1. Field of the Invention
The present invention relates to a vehicular power line communication system for superposing communication data among respective electronic control units (ECUs) on power lines for supplying electric power to respective instruments mounted on a vehicle, thereby making communication.
2. Description of the Related Art
In a vehicle in recent years, a power line communication system has been proposed in order to make data communication among various ECUs, for example, as disclosed in Japanese Patent Laid-Open Publication No. 2004-56197.
The power line communication system superposes communication data among ECUs mounted on the vehicle on power lines cabled in order to supply electric power to the respective ECUs, thus making it possible to reduce the number of harnesses connecting the respective ECUs to one another.
FIG. 1 is a block diagram showing a configuration of an ECU connected to the power line of a conventional power line communication system. As illustrated, an ECU 101 is coupled to a power line 105, and includes a transmission circuit 102 performing ASK (Amplitude Shift Keying) modulation, a reception circuit 103 performing ASK demodulation, and a CPU 104 for controlling transmission/reception of the data by the transmission circuit 102 and the reception circuit 103 and controlling loads (not shown) mounted on the vehicle.
Furthermore, the ECU 102 includes a band pass filter (BPF) 106 provided between the power line 105 for supplying a drive voltage (for example, 12V) to the ECU 101 and the transmission circuit 102 and the reception circuit 103, and a power supply circuit 107 for converting the drive voltage supplied through the power line 105 into a voltage of a desired level.
In the case of transmitting the data, transmission data, a carrier wave, a transmission permission signal and a standby signal are outputted from the CPU 104 to the transmission circuit 102, and the transmission data is ASK-modulated by the transmission circuit 102 and superposed on the power line 105.
Meanwhile, in the case of receiving transmission data transmitted from another ECU, which is superposed on the power line 105, this transmission data is captured into the reception circuit 103 through the band pass filter (BPF) 106 and ASK-demodulated there, and it is thus made possible to obtain reception data.
Moreover, the ECUs mounted on the vehicle tend to increase nowadays, in which plural communication areas are set, and power line communication using a PLC apparatus is made in each of the communication areas. Here, the PLC (Power Line Communication) is a mode of enabling communication without a dedicated line by superposing the communication data on the power line. FIG. 2 is a wiring diagram in the case where a first communication area 108a and a second communication area 108b are set for the power line 105.
As shown in this drawing, the first communication area 108a includes a junction connector 109 connected to the power line 105, and plural branch power lines 110 branched from the junction connector 109 are coupled to an ECU 101a serving as a master station and plural ECUs 101b serving as slave stations. Moreover, the respective ECUs 101b are coupled to loads 111 being objects to be controlled. Furthermore, the second communication area 108b also has a similar configuration to the above.
As described above, in the first communication area 108a, the data communication is made among the ECU 101a serving as the master station and the respective ECUs 101b serving as the slave stations through the branch power lines 110.